Energy saving window coverings

Use window coverings to keep the heat where you want it!

Energy saving window coverings can cut your home heating and cooling costs in a number of ways. They block the sun out in summer (when sunlight turns into unwanted heat), and allow sunlight in during the winter (when you want the solar heating). They improve insulation, creating an extra layer of still air between your windows and the indoors, cutting heat transfer in both hot and cold weather. And they control the amount of light coming in, so you can take advantage of natural lighting where possible, without at the same time losing heat to the outdoors in winter, or overheating the room on hot summer days.

Let’s start by going through the background on how energy saving window coverings help, then we’ll cover the different types of window coverings one by one:

• Energy saving curtains and drapes
• Energy saving window blinds
• Energy saving window shades
• Energy saving awnings
• Energy saving window overhangs
• Plastic window insulation kits
• Storm windows
• Other energy efficient window coverings

Types of energy efficient window coverings

Fitted window coverings. These energy saving window coverings create a dead air space between themselves and the window glass, significantly increasing the insulation value of the window covering, compared to window coverings with free airflow between the covering and the window. See the illustration under Energy saving drapes and curtains below.

ENERGY STAR window coverings: Window treatments are not part of the ENERGY STAR efficiency rating program, so you will not find any ENERGY STAR ratings on treatments such as curtains, blinds, awnings, or other window treatments. So use this page to find the most energy saving window coverings for your home.

Insulation R values of energy saving window coverings: Standard blinds and curtains have an insulating value of only R-1. Energy saving window coverings with an insulation layer, for example honeycomb blinds or curtains with an insulating lining, can have insulating values of up to R6. Rigid foam panels custom cut to the size of a window opening in a basement or other infrequently used room can have R-values up to the R-value of the panel itself. For example, my parents use a 2-inch thick layer of pink foam panels as the energy saving window coverings on the basement windows of their winterized cottage, giving an insulation value of R-8. It is not the most attractive energy saving window treatment but given that no one spends much time in the basement in winter the savings more than make up for the aesthetic impact.

Awnings and overhangs: These energy saving window coverings prevent hot summer sunlight from even striking the outside of your windows, while allowing the lower-angled winter sun into your home where the sunlight is converted to heat. Canvas awnings not only reduce the solar heat gain through a window in hot weather, but offer protection from sun and light rain when you are sitting out on a patio or deck covered with the awning.

Light-colored energy saving window coverings, whether inside or outside the windows, reflect sunlight and prevent it from heating up your home in the summer. These window treatments can be opened on colder days to allow solar energy to warm your home.

Some energy saving window coverings provide a layer of insulation, which prevents convection currents from carrying the room air past the window glass. If you use energy saving window coverings that cut down on convection, you can avoid heat transfer between the room and the outside, whether in summer or winter. The insulation value of energy saving window coverings can vary from none whatsoever to over R-10 for thick, custom-made rigid foam inserts.

Mesh window screens not only keep out unwanted insects in summer, but diffuse the sunlight entering your house, especially on east and west facing windows, reducing heat gain in summer. However, their effect on heat transfer is small enough that it’s a stretch to call them energy saving window coverings.

Where do your windows face? You’ll get the hottest light from west-facing windows so if you’re trying to keep your house cool, be sure to either use highly reflective energy saving window coverings, an awning, or energy-saving window film.

Remember to plan for natural lighting, so you can save on lighting costs as well as heating and cooling. South-facing windows provide the best natural light, so energy saving window coverings that reflect infrared radiation but allow some visible spectrum light in are the best.

Combine several kinds of energy saving window coverings to get the most energy efficient window treatments possible. For example, try putting exterior shutters on windows that have energy saving curtains, and you’ll get the benefit of both energy saving window coverings.

Energy saving curtains and drapes

Conventional drapes or curtains reduce heat loss from a room by only 10% because convection carries hot air between the curtain and the window, where the air loses heat, falls below the bottom of the curtain (and out the sides) and draws in more hot air above. (See the first window in the illustration at the right.)

Conventional drapes can easily be converted to energy saving drapes by restricting the air flow either at the top or bottom, as shown in the second window at the right. For example, by enclosing the drapery bars at the top to prevent air from entering behind the top of the curtains, or by ensuring the drapes go all the way to the floor, you will significantly cut the convection current and magically convert low-efficiency drapes to energy saving window coverings!

To get maximal efficiency though, it’s best to have the drapes snug on all sides, for example using velcro or magnetic tape on the side seams and on the walls at the outside edges of the curtain. Drapes that are snug against the wall and block vertical airflow as well cut heat loss up to 25%.

Medium colored drapes with a white plastic backing are best for keeping out the heat in summer. The white backing reflects sunlight back outside before it gets turned into heat, while the medium color allows enough natural light into the room to make the room usable without a light, without letting in enough to create heat.

When buying curtains, or fabric to make your own curtains, look for closed-weave fabric, which does a better job than open-weave fabric of restricting both airflow and light between the window space and the room space.

A double layer of drapes is more efficient than a single layer as more separate air spaces are created and convection is reduced.

Energy saving window blinds

Most window blinds save energy only as reflective barriers. That means they reflect summer sunlight back outside before it can strike objects inside the room and turn into heat; and to a much lesser extent, they can reflect infrared radiation back into a room in winter instead of allowing it to escape.

Standard window blinds can be quite effective at keeping your house cool in summer, reducing heat gain by up to 45%, but don’t do much for keeping the heat inside in winter, because they don’t provide much insulation value. That’s because they’re very thin, typically have many gaps between the vanes, allowing air to pass through the blinds, and aren’t sealed around the edges, allowing the cold window pane to cool the air between the window and the blind, causing it to fall out below the open bottom of the blind, which in turn draws warm air down from above the open top.

Energy saving window blinds are sometimes made in a honeycomb or cellular structure, so that an insulating air pocket separates the window air space from the room air space. When the blinds are closed the honeycomb is collapsed; when the blinds are open, the air pocket acts as insulation. Honeycomb blinds come in single- or double-honeycomb configurations; the double honeycomb provides a higher R-value. You cannot adjust honeycomb blinds to let in more or less light, other than by raising or lowering the entire blind.

Single- or double-layer honeycomb shades have an insulation value between R-2 and R-5. They can block up to 62 percent of heat transfer through the window.

Hunter Douglas has come up with a newer honeycomb shade design, the Duette Architella, in which one honeycomb is placed inside another honeycomb. In the opaque configuration (where the inner honeycomb is opaque mylar) these blinds can achieve an insulation value well over R-7, the highest in the industry.

You can also buy energy saving window blinds made of distinct vanes (similar to a standard window blind) but where the vanes provide some insulating value when closed. The first column in the illustration at left shows the blinds open, the second closed; in the third column the edges and filling have been made the same color so you can see how much of an insulation layer these blinds provide when closed. While the layer is thinner than that with honeycomb vines, the vanes can be sealed or even foam-filled which improves their R-value somewhat.

When closed, blinds provide similar reflective and insulating properties whether horizontal or vertical. However, horizontal blinds are better for allowing indirect daylight into your house in summer while blocking direct sunlight, which turns into heat inside your house.

Blinds are typically mounted inside the room in most houses in North America, but exterior, roller blinds are sometimes used in places where security is a concern, as they act as an additional entry barrier. However, exterior roller blinds don’t allow you to adjust the vanes to allow indirect sunlight; the only way to get natural daylight into the room in summer while preventing heat build-up is to open the blinds part way up. They also generally don’t do a good job of either providing insulation or blocking airflow between indoors and outdoors.

Energy saving window shades

Roller shades (single flexible sheets that roll down to cover a window, what we used to call ‘a blind’, as opposed to ‘blinds’, when I was a kid) are much more efficient than curtains and many louvered blinds, because they sit very close to the glass, restricting convection currents and thereby reducing heat exchange by up to 28%. If you seal the side edges of the roller shade, for example by using side tracks, you can reduce heat exchange by up to 45%.

Ideally, shades should be reversible, with a light, reflective side and a dark, heat-absorbing side. In cold weather the light, reflective side is placed facing inwards, so that the reflective side reflects the indoor heat away from the window and back into the room, while the heat absorbing side can convert visible-spectrum light from outside into heat. In warm weather the reflective side faces out so that sunlight does not warm the room.

If you have some skill with a sewing machine, you can make your own quilted roman shades out of cloth, and save a bundle on what it would cost you to have them made professionally, as well as save energy in your home. Terrell Sundermann teaches you exactly how to create window hangings, her combination of a wall hanging and a roman shade. This book gets great reviews from customers and is written in clear prose with excellent illustrations.

Energy saving awnings

If you want natural daylight in your house in summer but don’t want the heat build-up that comes from letting in direct sunlight, consider energy saving awnings as one energy saving window covering option. Awnings are especially efficient on west-facing windows (in the northern hemisphere), cutting solar gain by up to 77% by preventing visible-spectrum sunlight from striking the window glass, entering your house, and turning into infrared (heat) radiation. On south-facing windows they can reduce heat gain by 65%.

You can gain some of this energy saving benefit by installing windows with low-E coatings or by adding energy saving window film to existing windows, as the coatings do reflect infrared and some visible spectrum radiation instead of allowing it in. But one of the great things about energy saving awnings is that you can block out the sunlight and still leave the windows open to get a breeze through the house.

Window awnings come in two main formats: venation awnings, which contain a single sheet of material, usually retractable, and which block perpendicular sunlight only; and hood awnings, which have sides added to block out sunlight entering from the sides.

For south facing windows, hood awnings are more effective as they block sunlight throughout the day. Because the summer sun is high in the sky, south-facing awnings do not need to project much from the side of the house, and as a result the winter sun, which is much lower in the sky, can still strike the windows and add solar heat to your home.

I recommend retractable awnings over rigid hood awnings for west-facing windows because in winter you’ll want to retract the awnings to allow as much sunlight in as possible.

Modern awnings are typically made from long-lasting, water-repellant synthetic fabrics. These fabrics do not tatter or fray the way old, canvas coverings used to, and they are usually mildew and fade resistant. You should choose light-colored awnings of tightly woven fabric as these will reflect sunlight, while dark awnings will turn much of that sunlight into heat, which will warm the side of your house or enter the windows below or above the awning.

Energy saving window overhangs

If you are planning a new home, or putting on an addition, that has south-facing windows, consider designing energy saving window overhangs into the structure. A properly sized window overhang, such as an extended roof, extra-wide soffit, or an upstairs balcony over a downstairs window, blocks the direct sunlight from the hot summer sun, while allowing the lower-angled winter sun to shine in and warm your home.

You’ll need to take into account local site characteristics, so it’s best to involve a solar heating designer to help you account for factors such as the changing angle of the sun through the year, and the amount of solar radiation through different seasons.

Plastic window
insulation kits

Sealing your windows with plastic from the inside, for example with an energy saving window kit, can cut heat loss by up to 50%. The kit pictured on the left can seal up to 5 windows of 3 x 5 feet each. Other kits come in roll format or for larger windows or even patio doors.

You’ll find it easy to install these energy saving window coverings, available from several manufacturers (and sometimes as in-store brands at building centers). First, tape a continuous rectangle around the window frame with the double-sided tape. Next, cut the plastic to a size about an inch wider in each dimension than the taped rectangle. Remove the plastic backing to the double-sided tape, and carefully press the plastic onto the tape, first at the bottom, then at the top, then on either side. Don’t worry if it looks wrinkled, just make sure you get a tight seal all around. Finally, use a blow-dryer to heat the window up (be careful to hold the blow dryer at least 6 inches away from the plastic to avoid burning a hole in it). As the heat from the blow dryer gently heats the plastic, it shrinks to form a tight, wrinkle-free, air-tight barrier between the window and the sheet.

If you are careful removing the windows at the end of the heating season, you can reuse the kits for several years, although usually you will need more double-sided clear tape. I used to use these kits all over our leaky rental house, and I would either reuse a sheet for the same window, or if the edges got damaged removing it, use that sheet for the next smallest window it would fit. These plastic window insulation kits made a huge difference to my heating bill; after all, some of my windows were 3 x 6 feet!

Storm windows

I remember many cold, rainy autumn days spent up on a ladder at my parents’ house, when I was a teenager, helping my mother put up the storm windows around the upstairs rooms. My hands froze, but at least the storms kept us warm in our bedrooms through the winter.

Storm windows are an additional pane of glass that is either permanently affixed to the window opening, or put in place at the start of each heating season and removed at the end of the season. Most storm windows are affixed on the outside of the window frame. Exterior storm windows are very common in older houses where the windows have not been replaced with new, double-glazed energy efficient windows.

A storm window combined with a single-pane window can be up to 50% more energy efficient than the single-pane window alone. If you live in a cold climate and you have old, single-glazed windows without storms, you are probably losing a large percentage of your building’s heat through air leakage and convection to the outdoors.

For wooden storm windows, you can significantly improve their efficiency by adding sticky-backed foam tape weatherstripping to the inside of the storm, where it meets the window frame. This will create an air seal that prevents cold drafts from entering the house.

Aluminum storm windows consist of aluminum frames permanently attached to the window opening, where you can either permanently attach a fixed upper pane of glass and lower insect screen, and a sliding lower pane of glass, or a single sheet of glass that is removed at the end of each heating season to allow airflow in warmer months.

I highly recommend replacing old windows that require storms with new, energy efficient windows. It’s one of the best upgrades you can do for a home, in terms of cutting down on drafts as well as improving both your enjoyment of your home, and its resale value. I spent more on window upgrades in my home than on any other energy efficiency upgrade (over $6,000) and I don’t regret it one bit. Rooms that used to be freezing cold in winter became comfortably warm as soon as the new windows went in.

Other energy efficient window coverings

Window quilts make great energy saving window coverings; they are sealed on all sides and include an insulating layer and vapor barrier. They have an R value of up to R-5.

Hardwood shutters with foam cores and paneling have insulation values of up to R-3.2. Hardwood shutters with adjustable louvers, or wooden window blinds, have a much lower insulation value and the gaps between the louvers or slats let considerable airflow through. How energy efficient your foam-cored shutters are depends both on the snugness of the fit between the shutter edges and the window, and on the thickness and type of insulating foam used in the shutter.

Custom insulating shutters can be made for you to provide a high level of insulation and complete light blockage. These energy saving window coverings are usually made of insulation and a vapor barrier enclosed in decorated plywood or wood panels. This is an expensive option but can cut your heat loss by as much as 80%.

You can make your own energy saving window coverings out of rigid insulation foam. Cut the foam to slightly larger than the window opening (1/8th of an inch more) and press the foam rectangle into the window opening. This is a sensible way to make your own energy saving window coverings to reduce heat loss in winter in rooms that are not used much, such as a basement. Insulating panels can cut heat loss by up to 85%.